In the formation of color paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult and requires great care and expense to ensure proper laydown and cooling of the polyethylene layers.
In photographic papers the polyethylene layer also serves as a carrier layer for titanium dioxide and other whiting materials as well as tinting materials. By experience, it has been shown that a bluish tint is necessary as the background for images on paper type bases to obtain a favorable response from customers of these products. It would be desirable if the colorant materials rather than being dispersed throughout the polyethylene layer could be included in a layer of the photographic materials that is not subjected to the rigors of high temperature extrusion, which is the most common way of manufacturing the melt extruded polyethylene layer.
The high temperature processing of the polyethylene layer requires tint materials that are expensive because they must be chemically and color stable at temperatures typically over 290 degrees centigrade. It is common to incur clumping of the whitener and tint materials and it may be necessary to resort to special high temperature filtration to minimize objectionable clumping which is seen as undesirable spots in the image.
The compounding of the polyethylene, whiteners, and tinting agents is usually done far in advance of the extrusion of the layer on the base therefore, it is impossible to change the tint significantly if tint changes are needed to accommodate any colorimetric variations of the base materials or subsequent image forming layers.
It has been proposed in U.S. Pat. No. 5,866,282--Bourdelais et al., to utilize a composite support material with laminated biaxially oriented polyolefin sheets as a photographic imaging material. In U.S. Pat. No. 5,866,282, biaxially oriented polyolefin sheets are extrusion laminated to cellulose paper to create a support for silver halide imaging layers.
In European Application EP 585 679 A1, anthraquinone dyes are incorporated into emulsion interlayers as conventional oil and water dispersions. The anthraquinone dye dispersions used both ethyl acetate and a high boiling permanent solvent to dissolve the organic compounds prior to incorporation into the photographic emulsion coated on a support consisting of a high density polyethylene coated on a base paper. Incorporating oil and water dispersion pigments as disclosed in EP 585 679 A1 is undesirable because pigments, by nature, are insoluble, crystalline solids, which are the most thermodynamically stable form that they can assume. In an oil and water dispersion, they would be in the form of an amorphous solid, which is thermodynamically unstable. Therefore, one would have to worry about the pigment eventually converting to the crystalline form with age. A further problem with the use of ethyl acetate and a high boiling point solvent is that the high boiling solvent is not removed with evaporation, and it will cause unwanted interactions in the coating melt such as ripening of Ostwald oxidized developer scavenger of dispersion particles, or other components in the other imaging layers. It would be desirable if pigments could be incorporated into the imaging layers without the use of ethyl acetate and high boiling point permanent solvents.